For the production of batteries, such as lithium-ion batteries, standardly an active material layer is applied onto an electrically conductive current collector. As an active material layer, for example pastes containing graphite or nanocrystalline amorphous silicon having lithium deposits, or also pastes including mixed oxides containing lithium such as Li4Ti5O12, LiCoO2, LiNiO2, LiMn2O4, lithium iron phosphate (LiFePO4), or tin dioxide (SnO2), are applied onto a bearer foil acting as a current collector. As bearer foils, for example copper foils or aluminum foils can also be used. Bearer foils coated in this way can be used as negative electrodes (so-called anodes) and/or positive electrodes (so-called cathodes) in batteries, a separator being provided between the anode and the cathode. Electrode stacks (e.g. anode-separator-cathode) as a rule form a square packet. Alternatively, an anode-separator-cathode unit can be rolled up. The units are placed into a housing, e.g. in the form of a pouch.
The packagings obtained in this way are filled with an electrolyte. Suitable electrolytes include for example salts such as LiPF6 or LiBF4 in anhydrous aprotic solvents such as ethylene carbonate or diethylene carbonate, etc. Also suitable are polymers of polyvinylidene fluoride (PVDF) or poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) as well as lithium phosphate nitride (Li3PO4N). These can be present and used both in liquid form and as a gel or solid.
Via the electrically conductive arresters, which must have a cross-section adequate for the current strength that they are to handle, such a cell can be electrically contacted. This arrester thus also acts as terminal region.
For an efficient overall system, as a rule a plurality of small cells are connected together with a high wiring outlay. Alternatively, it is possible to produce correspondingly large-surface electrodes in order to avoid such a wiring outlay.
During the charging and discharging of such a battery, there is now the difficulty that the current produced incrementally in the surface of the electrode flows from all regions of the electrode in the direction of the current collector. As a result, the current density in the electrode increases continuously in the direction of the current collector.
Frequently, the current conducting is associated with losses that appear as a local heating of the battery. In particular, disturbance points in the ideal configuration, such as non-uniform coating, excessively large particles in the layer, non-homogenous pressing on of the electrodes, or the like, additionally cause a non-homogenous current flow in the electrode. This can therefore result in an overheating of the battery, locally or zonally, which can cause premature aging, loss of capacitance, or thermal damage to the battery.
Patent document DE 11 2012 000 876 discusses the use of a partly porous aluminum body as current collector. This body is obtained through electrochemical deposition of aluminum on a polymer foam, removal of the polymer, and partial compression of the aluminum network.
Patent document US 2014/0272561 discusses an electrode including a current collector having a network structure. The current collector can be produced by pressure or deposition methods.
Patent document US 2015/0125756 also relates to a method for producing an electrode in which a current collector is provided in the form of a network. The active material is subsequently applied thereon.
For reasons of stability, the known methods use either current collector foils having a sufficient layer thickness to be capable of being handled by machine without being destroyed, or include an additional bearer material. From the point of view of the performance of the electrode, however, a realization that is as thin as possible of the current collector is desirable, because this collector does not make any contribution to the actual energy storage. Instead, the current collector increases the volume and the weight of the battery, and thus reduces the achievable energy density of the battery. This object is achieved by the invention described below.